Collision avoidance methods currently employed in automobile adaptive cruise control (ACC) systems use radio detection and ranging (RADAR) or light detection and ranging (LIDAR) to measure range to targets from the front of the equipped vehicle. Because braking distance is in part a function of the equipped vehicle speed, the determination of collision risk in ACC is based at least partly on target range and equipped vehicle speed information. Higher equipped vehicle speeds require longer ranges to targets before the ACC intervenes to reduce vehicle speed. If the range is reduced by the introduction of a new target vehicle in front of the vehicle, speed is reduced to increase the range or stand-off distance.
Although the ACC method may reduce rear-end collisions by the equipped vehicle with a target vehicle in front (at zero azimuth), it is insensitive to vehicles at all other azimuths. The ACC method will not help prevent collisions resulting from laterally or obliquely approaching vehicles, as can occur at intersections or during lane changes. The absence of an omni-directional risk assessment is a deficiency common to all forward-looking ACC systems, and common as well to most human drivers, as human drivers suffer from an inability to visually attend to more than one event at a time. Human omni-directional risk assessment also suffers from the requirement to expend time in the shifting of attention between events. Thus, human drivers often get involved in accidents because they are paying attention to the wrong event, and because they often make mistakes in the determination and execution of the most appropriate avoidance response. This is particularly true when more than one critical obstacle event is involved.